1. Field of the Invention
The present invention relates to a powdery detergent composition comprising a nonionic surfactant as a main base, and more particularly to a powdery detergent composition which is free from bleeding of the nonionic surfactant, does not exhibit any deterioration in its solubility during storage and has an improved detergency against a fatty acid soil.
2. Description of the Related Art
A nonionic surfactant has various features such as good hard water resistance and, at the same time, prominent detergency and capability of dispersing soil, and further very excellent biodegradability, so that it is deemed to be an important surfactant for washing.
However, since many nonionic surfactants used for washing purposes are usually liquid at ordinary temperatures, a powdery detergent composition containing a liquid nonionic surfactant in a large amount has the problem that the nonionic surfactant gradually bleeds out from the powdery detergent composition with the passage of time and penetrates into the inside of the paper container which holds the powdery detergent composition or the powdery detergent composition brings about massive caking, which adversely effects the commercial value of the powdery detergent composition.
U.S. Pat. No. 4,138,051 (published on Jan. 23, 1979, Assignee: Henkel KGaA) discloses a detergent composition having an improved fluidity and comprising a premixture composed of a crystalline or amorphous aluminosiligate having an ion exchange capacity of 50 mg CaO/g (89 mg CaCO.sub.3 /g) or more (4% or less of a highly dispersive silica may be used as an oil-absorbent carrier), a nonionic surfactant and optionally aft inorganic peroxide capable of forming hydrogen peroxide in water and, incorporated into the premixture, a spray-dried detergent. Great Britain Patent No. 1474856 (published on May 5, 1977) discloses a detergent composition having an improved fluidity and comprising a mixture of a synthetic amorphous silica derivative (including an aluminosilicate) having an oil absorbability of 50 to 200 cm.sup.3 /100 g with a nonionic surfactant.
Thus the methods of improving the properties of a powder of a nonionic powdery detergent composition are known in the art. In the above-described prior art methods, however, since a water-insoluble carrier, such as silica, is used for the purpose of preventing the nonionic surfactant from bleeding and, at the same time, zeolite is incorporated therein for the purpose of improving detergency, the incorporation of an alkali builder is causative of a remarkable deterioration in the solubility of the nonionic powdery detergent composition after storage under high humidity conditions. This is believed to be because the alkali builder, which is a water-soluble silicate, serves as a binder for a water-insoluble substance such as silica or zeolite. Replacement of the zeolite with a phosphorus builder, such as sodium tripolyphosphate, is considered as a means for eliminating the above-described problem. This method, however, is not necessarily favorable from the viewpoint of environmental issue.
For this reason, in a zeolite-containing detergent composition, the amount of addition of a silicate builder such as JIS No. 1 sodium silicate is reduced to cope with the problem. However, the reaction in the amount of incorporation of the silicate builder leads to a lowering in the detergency, so that an improvement in the detergency is desired in the art. In fact, the above-described conventional detergent compositions have not always been useful for removing a fatty acid soil amounting to 10 to 20% of the dirt from the neck of cloths.
Further, WO 90/00189 (published on Jan. 11, 1990) discloses a granular detergent composition produced by homogeneously mixing a porous silicate derivative such as zeolite, bentonire and layer silicate with a water-soluble or water-dispersive nonionic surfactant in such a proportion that the porous silicate derivative content is 30% by weight or more. The layer silicate described in WO 90/00189, however, has a low ion exchange capacity. Further, the granular detergent composition has the problem of retaining solubility after storage for a long period of time and is unsatisfactory in the detergency as well.